The invention relates to contact lenses. In particular, the invention relates to contact lenses that have a back edge designed so that the flat portion of the edge does not rest on the wearer""s conjunctiva. The lenses of the invention exhibit good lens handling as well as excellent on-eye comfort and movement.
The use of contact lenses for cosmetic effect and the correction of visual acuity is well known. One disadvantage of contact lenses is that they are subject to debris accumulation while in use. Debris removal, in part, is facilitated if the lens moves easily on the eye because such movement allows tear fluid to remove debris from under the lens. However, the design of the back surface edges of most conventional contact lenses is flat, hindering movement of the lens on the eye. Additionally, the back surface edge of these conventional lenses may form a sharp edge that impinges on the conjuctival membrane, indenting and roughening the membrane.
One lens design, disclosed in U.S. application Ser. No. 09/277,464 incorporated herein in its entirety by reference, permits tear movement, debris removal, and does not impinge on the conjunctival membrane. Such a lens design, an edge-off-eye design, is depicted in FIG. 1 in a magnified, cross-sectional view that incorporates a fillet and edge flat. By xe2x80x9cfilletxe2x80x9d is meant a rounded junction between the back curve of the concave surface and the edge flat that is tangential to the back curve and edge flat. By xe2x80x9cedge flatxe2x80x9d is meant a flattened area connecting the back with the front surface of the lens.
Referring to FIG. 1, back surface 1 incorporates fillet 2 and edge flat 3 at its periphery to produce an edge-off-eye lens edge. This edge design permits lifting of the edge apex off of the ocular surface facilitating movement of the lens on the eye. Also, the shape of fillet 2 is such that is will not irritate the eye""s surface. The use of an edge flat 3 also truncates the lens edge, eliminating any sharpness from the lens edge.
Although the edge-off-eye design represents an improvement compared to conventional lens designs, problems with conjunctival indentations, and less than desirable on-eye movement can occur with edge-off-eye lenses. Thus, a need exists for an improved edge-off-eye lens.